Davis disclosed in U.S. Pat. No. 4,076,632 issued Feb. 28, 1978 a liquid fabric softening composition comprising cationic fabric softener, protonated di-polyethoxy monoalkyl amine, urea, and water. Among Davis' cationics were quaternary ammonium salts, quaternary imidazolinium salts, and mixtures thereof. Solvents such as alcohols, glycols and glycol ethers were used optionally.
Particular merit has been found for utilizing certain mixtures of quaternary ammonium salts with quaternary imidazolinium salts. Imidazolinium salts are superior to ammonium salts in softening ability on synthetic fabrics such as polyester and cotton/polyester blends, and are also superior in antistat properties which are particularly important for fabrics containing synthetic fibers. However imidazolinium salts tend to be more expensive than ammonium salts, and hence a mixture of the two types represents a good economic balance. However a pH-incompatability problem has now been found with certain compositions that utilize imidazolinium salts, and a pH of about 5.5 and below is desired. However, a pH below about 3.5 causes urea to become unstable and release ammonia, which causes not only an odor frequently considered unpleasant but also a diminution of the freeze-thaw stability that the urea was used to achieve. Complete replacement of urea with solvents, in conjunction with the protonated di-polyethoxy monoalkyl amine, provides the required freeze-thaw stability at these unusually low pH's.